1. Field of Invention
This invention is concerned with the display in color of variables which may be presented as waveforms and graphs. It is also concerned with the combined display, for visual appraisal, of several quantities which are different functions of the same variable or variables.
2. Description of Prior Art
In several branches of science useful conclusions can be drawn from variations of several quantities as a function of a common variable. One example is in seismic exploration, where the geological value of the conventional display of seismic vibration as a function of reflection time may be enhanced, by adding to the display further variables (such as interval velocity). Another example is in the interpretation of acoustic, electric, neutron and other logs taken in a borehole as a function of depth. Another example is in the interpretation of gravity and magnetic field readings taken as a function of distance along a profile. Another example is in the interpretation of medical waveforms (such as electroencephalographic signals as a function of time). Another example is in the formulation of a fault-condition diagnosis from a number of transducers (which may be in an engine, or a computer, or in the human body).
Where the expected nature of the relationship between several functions can be expressed mathematically, it has been usual to employ the techniques of cross-correlation to obtain a numerical measure of this relationship. In appropriate applications these techniques were very powerful, being able to find relationships between functions when such relationships could not be detected by visual examination of the corresponding waveforms. However, cross-correlation techniques were better than visual examination only if the integration intervals were long enough to include many cycles of variation and if there is no significant variation of the common-variable axis. Further, the need for visual correlation remained in every case where a skilled human judgment had to be made on the significance of the correlation, and where this skill had not yet advanced to the stage where the basis for judgment could be quantified. These situations existed in the aforementioned examples of geology, log analysis, medicine and brain research, and in other technological arts.